We have undertaken a series of investigations aimed at improving the precision of diagnosis and classification of human lymphoproliferative disease. Our approach is based on determination of lineage and differentiation through the use of monoclonal antibodies, flow cytometry and molecular genetics. As a result of these studies, we have demonstrated a phenotypic definition of clinically relevant classes of lymphoma and have identified cellular marker combinations that distinguish between benign and malignant processes. Monoclonality was found in nearly all malignant lymphoid neoplasmsn by Southern blot hybridizaton by the detection of gene rearrangements. However, we have discovered that monoclonality itself is not pathognomonic of malignancy since some types of nomalignant lymphoid proliferations consistently exhibit monoclonality. In other studies concerning cellular lineage, DNA from patient biopsies tested for T-cell receptor gene rearrangements revealed a lack of rearrnagement in nearly all B-cell neoplasms, clonal rearrangement in angioimmunoblastic lymphadenopathy (AILD), Ty lymphoporliferative disorder and mature T-cell neoplasms, and a hierarchy of surface molecule expression and genes rearrangement in neoplasms of T-cell precursors. Despite advances in the cellular origins of non-Hodgkin's lymphoproliferative disease, the lineage and clonal derivation of Hodgkin's disease remains largely unknown. Studies have been hampered by the lack of purified malignant cells from Hodgkin's tissues. We have prepared high enriched Hodgkin's cell suspension from several patients and are analyzing them for DNA rearrangement, viral genomes and expression of mRNA and protein.